1 files changed, 167 insertions, 0 deletions
diff --git a/Tools/Hazel-Networking/Hazel/Udp/UdpConnection.KeepAlive.cs b/Tools/Hazel-Networking/Hazel/Udp/UdpConnection.KeepAlive.cs
new file mode 100644
index 0000000..75b4f1d
--- /dev/null
+++ b/Tools/Hazel-Networking/Hazel/Udp/UdpConnection.KeepAlive.cs
@@ -0,0 +1,167 @@
+using System;
+using System.Collections.Concurrent;
+using System.Diagnostics;
+using System.Threading;
+
+
+namespace Hazel.Udp
+{
+    partial class UdpConnection
+    {
+
+        /// <summary>
+        ///     Class to hold packet data
+        /// </summary>
+        public class PingPacket : IRecyclable
+        {
+            private static readonly ObjectPool<PingPacket> PacketPool = new ObjectPool<PingPacket>(() => new PingPacket());
+
+            public readonly Stopwatch Stopwatch = new Stopwatch();
+
+            internal static PingPacket GetObject()
+            {
+                return PacketPool.GetObject();
+            }
+
+            public void Recycle()
+            {
+                Stopwatch.Stop();
+                PacketPool.PutObject(this);
+            }
+        }
+
+        internal ConcurrentDictionary<ushort, PingPacket> activePingPackets = new ConcurrentDictionary<ushort, PingPacket>();
+
+        /// <summary>
+        ///     The interval from data being received or transmitted to a keepalive packet being sent in milliseconds.
+        /// </summary>
+        /// <remarks>
+        ///     <para>
+        ///         Keepalive packets serve to close connections when an endpoint abruptly disconnects and to ensure than any
+        ///         NAT devices do not close their translation for our argument. By ensuring there is regular contact the
+        ///         connection can detect and prevent these issues.
+        ///     </para>
+        ///     <para>
+        ///         The default value is 10 seconds, set to System.Threading.Timeout.Infinite to disable keepalive packets.
+        ///     </para>
+        /// </remarks>
+        public int KeepAliveInterval
+        {
+            get
+            {
+                return keepAliveInterval;
+            }
+
+            set
+            {
+                keepAliveInterval = value;
+                ResetKeepAliveTimer();
+            }
+        }
+        private int keepAliveInterval = 1500;
+
+        public int MissingPingsUntilDisconnect { get; set; } = 6;
+        private volatile int pingsSinceAck = 0;
+
+        /// <summary>
+        ///     The timer creating keepalive pulses.
+        /// </summary>
+        private Timer keepAliveTimer;
+
+        /// <summary>
+        ///     Starts the keepalive timer.
+        /// </summary>
+        protected void InitializeKeepAliveTimer()
+        {
+            keepAliveTimer = new Timer(
+                HandleKeepAlive,
+                null,
+                keepAliveInterval,
+                keepAliveInterval
+            );
+        }
+
+        private void HandleKeepAlive(object state)
+        {
+            if (this.State != ConnectionState.Connected) return;
+
+            if (this.pingsSinceAck >= this.MissingPingsUntilDisconnect)
+            {
+                this.DisposeKeepAliveTimer();
+                this.DisconnectInternal(HazelInternalErrors.PingsWithoutResponse, $"Sent {this.pingsSinceAck} pings that remote has not responded to.");
+                return;
+            }
+
+            try
+            {
+                this.pingsSinceAck++;
+                SendPing();
+            }
+            catch
+            {
+            }
+        }
+
+        // Pings are special, quasi-reliable packets. 
+        // We send them to trigger responses that validate our connection is alive
+        // An unacked ping should never be the sole cause of a disconnect.
+        // Rather, the responses will reset our pingsSinceAck, enough unacked 
+        // pings should cause a disconnect.
+        private void SendPing()
+        {
+            ushort id = (ushort)Interlocked.Increment(ref lastIDAllocated);
+
+            byte[] bytes = new byte[3];
+            bytes[0] = (byte)UdpSendOption.Ping;
+            bytes[1] = (byte)(id >> 8);
+            bytes[2] = (byte)id;
+
+            PingPacket pkt;
+            if (!this.activePingPackets.TryGetValue(id, out pkt))
+            {
+                pkt = PingPacket.GetObject();
+                if (!this.activePingPackets.TryAdd(id, pkt))
+                {
+                    throw new Exception("This shouldn't be possible");
+                }
+            }
+
+            pkt.Stopwatch.Restart();
+
+            WriteBytesToConnection(bytes, bytes.Length);
+
+            Statistics.LogReliableSend(0);
+        }
+
+        /// <summary>
+        ///     Resets the keepalive timer to zero.
+        /// </summary>
+        protected void ResetKeepAliveTimer()
+        {
+            try
+            {
+                keepAliveTimer?.Change(keepAliveInterval, keepAliveInterval);
+            }
+            catch { }
+        }
+
+        /// <summary>
+        ///     Disposes of the keep alive timer.
+        /// </summary>
+        private void DisposeKeepAliveTimer()
+        {
+            if (this.keepAliveTimer != null)
+            {
+                this.keepAliveTimer.Dispose();
+            }
+
+            foreach (var kvp in activePingPackets)
+            {
+                if (this.activePingPackets.TryRemove(kvp.Key, out var pkt))
+                {
+                    pkt.Recycle();
+                }
+            }
+        }
+    }
+}
+\ No newline at end of file